Laminar flow fluid filter

ABSTRACT

A stacked washer multi-stage impaction and diffusion filtering apparatus wherein a succession of laminar flow channels terminated by impact target surfaces are arranged to form intricate channel systems on individual filter washers, the washers then being stacked to form a plurality of filter passages. The intricate channel system permits establishment of a large number of filtration stages within a given volume.

1 Oct. 24, 1972 United States Patent Bode M RY. mm DB m WD mm m RJ A: mm

n We L.m Mm

XX 64 30 33 0O 22 mn mm 33 LG 00 74 99 1. 37

Mich.

[73] Assignee: The Bendix Corporation [22] Filed:

Primary Examiner-Frank A. Spear, Jr. Attorney-William F. Thornton andFlame, Hartz, Smith & Thompson Dec. 22, 1969 [21] Appl. No.: 887,102

[57] ABSTRACT A stacked washer multi-stage impaction and diffusionfiltering apparatus wherein a succession of laminar [52] US.Cl.....,..............................210/322, 210/488 [51] Int. Cl.43/00 .210/320, 322, 294, 336, 488

flow channels terminated by impact target surfaces are [58] Field ofSearch......

arranged to form intricate channel systems on individual filter washers,the washers then being stacked to form a plurality of filter passages.The intricate channel system permits establishment of a large ReferencesCited UNITED STATES PATENTS number of filtration stages within agivenvolume. .210/488 3,397,794 8/1968 Toth et al. 3,450,264 6/1969 Graybill....210/32O X 18 Claims, 9 Drawing Figures PATENTEDUEI24 I972 SHEET u 43.700.111

I N VENTOR.

. Jay/b Fluid filtering requirements continually become more stringentas levels of industrial pollution increase. In addition, modern fluidicand pneumatic devices require ever increasing levels of purity fordependable operation. To meet these increasingly rigorous requirements,filters must remove particles of ever decreasing size. The greatest needfor improved filter devices is for liquid and gas filter units capableof removing extreme ly small particles such as those between 0.1 and 10microns in diameter.

Particles are seldom perfectly spherical and thus do not really havediameters. However, for the mathematical computations involved in mostfilter system planning, it is helpful to assume particles are sphericaland do have diameters. When speaking of particle size, I shallhenceforth presume that every particle can be assigned a diameter. I

I Few commerically available filters areeffective when particles aresmaller than 5 microns in diameter, and those that are effective areoften large and cumbersome. Among the known filtration methods forpurifying liquid or gaseous fluid flow are gravitational settling,sieving with woven or electroformed screens, centrifugal separation,interception, electrostatic removal, diffusion, and impaction. Many ofthese filtration methods are not capable of removing particles in the 10to 0.1 microns diameter range.

The gravitational settling technique is unreliable for particles of lessthan 40 microns diameter. The velocity of the fluid flow within most.filters is adequate to prevent the gravitational settling of anysmaller particles.

Sieving techniques are impractical when the particle diameter is below40 microns. Sieving requires the use of fine mesh screens to accomplishthe filtering operation. Successful sieving is complicated by the factthat particle shapes are irregular and screen openings are usuallysquare or rectangular. It is further complicated by the fact that thereare limits to how small screen openings can be made. The use of a screenoften encourages build-up on the screen of a layer of silt called afilter cake. This layer can produce undesirable pressure drops acrossthe screen which may damagethe screen since fine mesh is easily damaged.As a result, sieving has been found impractical for particles of lessthan 40 microns diameter.

Centrifugal separation devices filter by forcing the fluid into circularor spiral paths. Centrifugal forces in the filter exert greater outwardforces on particles than on fluid molecules since particles havesubstantially more mass. Particles are thus forced radially outward andlodge against the outer surfaces of the curved passages where adhesiveforces between particles and passages retain them. This separationtechnique removes particles as small as 10 microns diameter but isimpractical for smaller particles.

The interception method of filtration removes particles by making themcontact a post or other intercepting element in the flow stream. Thismethodfunctions effectively only when the diameter of the interceptingelement is smaller than the diameters of the particles to be removed. Ifthe diameter of the intercepting element is not smaller, the flowvelocity must be very high to b- 2 tain efficient filtering. It isdifficult to make interception elements of small enough diameter to beuseful when extremely small particles must be removed. In addition, theparticle must still contact the element and if it does not, there is nochance of removal. The interception method is effective in removingparticles as small as 0.5 microns diameter.

Electrostatic removal can separate particles of 1 micron and largerdiameters from fluid, but to be effective, the particle should becharged and must be brought into contact with a charged collectingelement.

Electrostatic removal is theoretically helpful for removing particles inthe 10 to 0.1 microns diameter range, but natural electrostatic chargingis unreliable since appreciable time is required for particles toacquire adequate charges even when passed through a charging region, andthe magnitude of each charge is affected by a particles size anddielectric properties.

Diffusion filtering is an-extremely effective method forremovingparticles of less than 0.1 microns diameter. Diffusion removal dependson the wayward motion added to a particles direct movement due tobombardment by fluid molecules. This bombardment, which is known asBrownian movement, is effective only when particles are smaller than 0.1microns diameter. Diffusion collection, then by its very nature, islimited to very small particles, i.e., less than 0.1 microns indiameter. Diffusion filtration can occur at any fluid velocity butbecomes increasingly efficient as velocity decreases. If the fluidvelocity can be made low enough, the efficiency of filtration can bemade to approach percent. The term efficiency refers to the ratio ofparticles removed from the fluid during filtration to particles in thefluid prior to filtration.

impaction filtering is an excellent method for removing particlesranging from 100 to 0.1 microns diameter. In the prior art, impactionfiltering has been accomplished by cumbersome impact baffles andlabyrinthine mazes which guide flowing fluid on collision courses withthe impact baffles. The prior art procedure has been to guide the fluidinto collision with a large number of baffles, and this collisionprocess is repeated until the desired degree of filtration has beenobtained. This procedure is adequate if particle sizes are larger than2.5 microns, but smaller particles often flow between baffles instead ofcolliding with them. The effectiveness of these prior art impactfiltering devices has always been reduced by turbulence occurring priorto the impaction and such turbulence has been virtually accepted andignored. This turbulence greatly decreases filtering efficiency becauseturbulent flow prior to impaction causes flowing fluid to retain andcarry particles around the impact surface rather than allowing them tocollide with the surface. It is desirable to diminish these turbulenteffects as much as possible. By doing so, impaction efficiency can beincreased substantially and filtering improved greatly. The presentinvention overcomes this turbulence problem.

T Another shortcoming of prior art impact filters is that these filtersare often large, and unusable in applications where compactness is afactor. The present invention is embodied in a filter which is extremelycompact, light, and easy to build.

SUMMARY OF THE INVENTION This invention comprises a filtration systemfor the removal of particles from flowing fluids, and can be adapted toremove a wide range of particle sizes. The invention utilizes a laminarflow channel to establish laminar fluid flow and at a point near the endof the channel where flow has become laminar, removal means extractcontaminant particles. The removal means may utilize impaction,interception, diffusion, gravity settling, or centrifugal separation.Laminar flow has been found to substantially improve filteringefficiency with each of these filtration methods.

This invention is shown embodied in an apparatus for removing extremelysmall particles of 0.1 through microns diameter from flowing fluid. Theterm particles as used herein applies not only to solid contaminants butalso to droplets of liquid or mist. Filtering action in the shownembodiments is accomplished principally by impaction filtering. However,the apparatus also utilizes the diffusion filtering method to provideadditional filtration. The invention, if desired, can be adapted toremoving larger particles of any desired size.

lmpaction filtering is an effective method for removing particles fromfluid if the particles collide with an impact target surface. Ifparticles collide, they attach themselves to the impact target surfaceand are retained by adhesive forces between surface and particles.Impaction becomes an increasingly undependable process, however, if thefluid flow is turbulent when it reaches the impact target surface. Inturbulent regions, velocities within the flow stream are random, andparticles move in every direction. As a result, many particles have nocomponent directed toward the impact target surface, and the randomvelocity of the fluid can often carry such particles around the impacttarget surface without collision. This turbulence is a major shortcomingof prior art impaction filters. Impaction filtering efficiency issubstantially improved by this inventions unique combination of flowpassages which is designed to greatly diminish turbulence byestablishing laminar fluid flow prior to each impaction. Establishmentof laminar flow causes a greatly increased number of particles tocollide with impact target surfaces and thus be removed from the fluid.To establish laminar flow, the invention utilizes straight, smooth flowpassages of ample length to eliminate the turbulence ordinarily occuringprior to impaction in prior art filters. It also has an intricate systemof connecting passages which, among other things, permit establisment ofa maximum number of impactions in a given space.

For purposes of this invention, the term laminar flow refers to flow inwhich there is little or no turbulence. In turbulent flow, the fluidvelocity at any fixed point fluctuates with time in a nearly random way.In any physically realizable system, turbulence is never completelyeliminated. Herein I describe as laminar any flow that is substantiallyfree of turbulence.

Improved impaction filtering is accomplished by guiding the fluid alonga laminar flow passage to establish laminar flow, and then allowing thisfluid to collide with an impact target surface which is positioned atthe downstream end of the laminar flow passage.

Although impaction is the principle filtration method used in myinvention, diffusion is utilized to further increase filtrationefficiency. After each impaction of fluid against an impact targetsurface, my unique channel system divides the fluid flow into twoseparate streams of fluid, each flowing at approximately half thevelocity prior to impaction. This reduction in velocity greatly improvesdiffusion filtering. The reduced flow velocity continues until the fluidhas been conducted to the upstream end of a laminar flow passage of thenext filtration stage. At that point, pairs of such lowered velocityflow streams are combined, and the original higher velocity existantprior to the previous impaction is restored so as to provide moreeffective impact filtering at the next impact target surface. Afterbeing combined, the united fluid stream is channeled into the upstreamend of another laminar flow passageto establish laminar flow. At thedownstream end of this laminar flow passage, when flow is essentiallylaminar, the fluid is impacted against an impact target surface. Thisfiltration process is repeated again and again until fluid has beenfiltered to the desired degree of purity. The filtration action of myapparatus will be discussed instill further detail hereafter.

The invention is shown embodied in a system of thin annular washerswhich can be compactly aligned to form a stacked washer filter element.An intricately designed system of filter channels is formed on onesurface of each washer. Two basic channel design systems are disclosed.The washer stack can be easily disassembled for cleaning and need not bediscarded when saturated with contaminant particles.

Washers can be fabricatedof materials capable of withstanding hightemperatures and pressures. When appropriate materials are selected, thefilter can be used in situations requiring temperatures as high as 1000Centigrade. Pressure differentials as high as 5,000 psi across thewasher stack present no collapse problem. The invention can, if desired,be embodied so as to Withstand even greater temperatures and pressures.

It is desirable fora filter to be operational regardless of thedirection of flow. Accordingly, the present invention functions equallywell when the direction of fluid flow is reversed.

It is also desirable that-each filter stage be protected from frequentclogging. To accomplish this objective, the invention has an alternativeflow channel at every stage of the filter. In the event a single channelbecomes obstructed, there is always an alternative path for the fluid tofollow. This uniquely designed filter system thus prevents most cloggingproblems commonly occurring with other filters.

Still other advantages of the invention are that it is durable, compact,resistant to shock and rough handling, easy to manufacture, and simpleto assemble.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded sectional viewof a stacked washer filter embodying the present invention.

FIG. 2 is an enlarged top view of a filter washer plate having a novelfilter channel system embodying the invention and usable in the filterof FIG. 1.

FIG. 3 is a further enlarged top view of a portion of FIG. 2 showing alaminar flow channel terminated by one type of impact target surface.

' FIG. 4 is an enlarged top view of a laminar flow channel like that ofFIG. 3 terminated by a different type of impact target surface.

FIG. 5 is an enlarged top view of a laminar flow channel like that ofFIG. 3 terminated by still another type of impact target surface.

FIG. 6 is an enlarged edge view of three stacked washers like those inFIG. 2 showing openings for fluid to enter the channel systems of thewasher stack.

FIG. 7 is an enlarged top view of a filter washer plate like that shownin FIG. 2 having a second type of filter channel system embodying theinvention.

FIG. 8 is an enlarged top view of a portion of the washer plate shown inFIG. 7.

FIG. 9 is an enlarged top view of a portion of a washer plate in whichthe effective diameter of passages is not uniform throughout the filter.

DESCRIPTION AND OPERATION OF THE PREFERRED EMBODIMENTS The invention isshown in FIG. 1 embodied in a stacked washer fluid filter assemblyindicated generally at 10. The filter assembly 10 has a head 12 and acasing 14. The casing 14 has casing threads 15 which cooperate with headthreads 17 to attach the head 12 to the casing 14 and provide a fluidtight seal. An inlet passage 20 in the head guides incoming fluid to areservoir 22; the reservoir occupies much of the interior of both thelower casing 14 and the head 12. A washer stack 24, formed of thin flatannular filter washers, such as washers 25 and 26, having a system offlow channels 27 thereon, is positioned within the reservoir 22. Themany washers of washer stack 24 are aligned and centered about a rod 28which is passed through the core 30 of each washer. The washer stack 24may contain several thousand filter washers depending on the quantity offluid to be filtered.

A hole 34 is bored diametrically through the upper end of the rod 28,and pin 36, which is passed through hole 34, cooperates with annularridge 38 in upper collar 40 to hold the upper end of rod 28 to uppercollar 40 when the washer stack 24 is fully assembled. The diameter ofrod 28 is selected to permit ample clearance between it and washer stackcore 32 so fluid can flow from washer stack core 32 through collar 40,and finally into outlet passage 42.

The lower end of rod 28 is provided with rod thread 44. When theindividual washers are properly aligned about rod 28, a lower collar 46is placed in communication with the lower face of the bottom washer 26of the stack 24 and rod nut 48 is tightened securely onto rod thread 44until the individual filter washers 26 are securely compressed againstone another. The lower collar 46 distributes the force evenly over thesurface area of the lowest washer 26.

When the parts of filter assembly 10 are assembled and the casing 14threaded into head 12, casing spring 50 keeps upper collar 40 of washerstack 24 in mating relationship with outlet tube 41. Upper collar 40 isprovided with a gasket 51 to provide a fluid tight seal between theoutlet tube 41 and upper collar 40.

FIG. 2 is an enlarged top view of a filter washer plate like that shownat 25 in FIG. 1. Filter washer plate 25 (FIG. 2) is shown as a thin flatannular disc having a central core 30, an outer edge 58, and anintricate flow channel system 27 formed in a flat first surface 60. The

flat lower face or second surface (not shown) has no channel system andacts as closure means for the flow channel system of an abutting lowerfilter washer plate such as plate 26 (FIG. 1). The washer channel systemof the invention can be formed on or in almost any body or on or in anyplate and does not require an annular washer. A body, either unitary orwith a plurality of parts, can contain the channel system. Any plateseated against the channel system side of a filter plate can provideclosure means for the channels thus forming a system of passages.

The filter channel system 27 can be formed as a system of passageswithin a body. If desired, a channel system such as system 27 can beformed on both first and second surfaces of the filter washer plate 25(FIG. 2). When assembled into a washer stack, such washers would bespaced from one another by a blank washer (not shown), i.e., withoutchannels on first and second surfaces.

The flow channel system 27 shown in FIG. 2 is most easily understood ifone first examines a single filtration structure located thereon. Eachfiltration structure consists of three basic elements, namely a laminarflow channel, a connecting channel which intersects the laminar flowchannel, forms an impact target surface at its intersection therewith,and extends between the laminar flow channels of two successivestructures (if there are successive structures), and closure means tocover the channels and thereby convert them to passages which preventescape of flowing fluid. It should be understood that the impact targetsurface is but one type of removal means, and that other types ofremoval means can readily be substituted for the impact target surfaceas'will be explained in further detail hereafter. I have shown myinvention embodied in an impaction filter because impaction is anexcellent filtration method to remove particles in the size range whichtoday presents the greatest challenge to the filter art.

Referring to FIG. 2, a typical filtration structure has a laminar flowchannel 112, a connecting channel 113, and an impact target surfacelocated adjacent point 116. Connectingchannel 113 extends from point115, where it joins the upstream end of a successive laminar flowchannel 122 associated with filtration structure to point 215 where itjoins a laminar flow channel 222 associated with an identical filtrationstructure 220. Closure means are here provided by the second surface 29(FIG. 1) of an adjacent washer. Filtration structures 110 and 210 (FIG.2) make up a filtration stage, namely, the second stage of the filtersystem as will hereafter be explained in more detail. Every filtrationstructure of the many structures which form the intricate flow channelsystem 27 of washer 25 functions in the same way and has elementsidentical to those just described. The width and depth of individualchannels remain constant throughout the channel system shown in FIG. 2although this is not essential, as will be discussed hereafter.

FIG. 3 is an enlarged top view of a portion of filter structure 110showing laminar flow channel 112, connecting channel 113, and the impacttarget surface adjacent point 116. The function and operation of eachelement of the structure 110 will now be explained in detail using FIG.3. The following explanation presumes that closure means is present toprevent fluid from escaping from the open channels, but in the interestof clarity such means is not shown in FIG. 3. It is to be understood,however, that when in operation the channels must be covered toformpassages. In the following explanation of FIG. 3, Ishall refer tothe channels as channels. However, when closure means is applied to theopen channels or when the channels are inside a body they becomepassages. Although FIG. 3 is an enlargement of a structure shown on thewasher of FIG. 2, it should be added that the details of construction,design, and operation are equally applicable to the filtrationstructures shown in FIG. 7 and 8 which will be explained in detailhereafter. The connecting channels in FIG. 3 are shown only in part. Thefiltration structure indicated generally at 110, has a laminar fiowchannel 112 and a connecting channel 1 13 intersecting the laminar flowchannel 1 12. Fluid enters the filtration structure 110 nearpoint 105,where connecting channels 103 and 2030f a previous filtration stage jointhe upstream end of laminar flow channel 112. The direction of fluidflow in filter structure 1 is indicated by flow arrow. 1

At the downstream end of laminar flow'channel 112, connecting channel113 not only intersects channel 112 to conduct fluid to successivefiltration structures, but also provides removal means in the form of animpact target surface adjacent point 116 opposite the downstream end oflaminar flow channel 112.

It has been found that the best impaction filtering is obtained when animpact target surface terminatesa region of laminar flow. Accordingly,laminar flow channel 112 is carefully designed to insure thatfluidflowing therein will attain laminar flow characteristics by the time itreaches the downstream end of channel 112. Laminar flow channels shouldbe straight, smooth, and free of obstructions because curvature,roughness, or obstructions can generate-turbulence. To be certain thatflow is substantially laminar by the time it reaches the end of thechannel 112, the channel 112 should be substantially straight with alength to effective diameter ratio of at least 10 to 1. It has beenfound that'ratios between 20 to I and 30 to 1 establish excellentlaminar flow. The term effective diameter refers to the diameter of acircle encompassing an area equal to the cross sectional area of thelaminar flow channel. It is not essential that each laminar flow channelhave the same length, but for convenience of placing it on a filterwasher surface, it is sometimes helpful.

Once laminar flow has been established, particles in the fluid travel atessentially the same velocity as the fluid. When the fluid flowing inlaminar flow channel 112 reaches the intersection with connectingchannel 113, the fluid is forced to divide substantially equally to leftand right. The momentum of most particles traveling with the fluid issufficient to prevent them from being carried with the fluid around thecorners 117. As a result, many of these particles collide with thesurface region opposite the downstream end of laminar flow channel 112.This surface region is herein called an impact target surface. Particlescolliding with the im-' pact target surface adjacent point 116 adherethereto due to adhesive force between particles and surface commonlyknown as van der Waals force. An accumulation of particles on the impacttarget surface of filtration structure 1 10 is shown at 118.

When fluid initially enters the upstream end of laminar flow channel 112the fluid flow is turbulent. As it proceeds along the laminar flowchannel v112 it gradually becomes laminar. The only turbulence which canbe expected in laminar flow channel 112, once initial turbulence hassubsided, is small amounts of turbulence generated by minor surfaceirregularities on the inside surface of the channel. For our purpose,these effects are negligible, and flow at the downstream ends of laminarflow channels can be described as laminar. As the fluid reachesconnecting channel 113 and divides to left and right to follow channel113, some turbulence is introduced. The presence of a turn'alwaysgenerates turbulence. This turbulence, however, at operating velocitiesand pressures will be confined to connecting channel 113 and will notadversely affect the laminar flow in laminar flow channel 112.

Flow leaving laminar flow channel 1 12 is divided into two substantiallyequal flow streams as it enters connecting channel 113 in order toreduce the velocity of :the fluid flow. This reduction in velocity helpsto minimize the level of turbulence adjacent to impact target surface116. Since the width and depth dimensions of channel 1l 3.areessentially equal to those ofchannel 112, the fluid velocity inchannel113 is approximately half the velocity of fluid flow in laminar flowchannel 112. In short, velocity has been halved by doubling the total,cross sectional area-of flow channels; since fluid leaving laminar flowchannel 110 encounters twice as much channel volume as it entersconnecting channel 113, the flow velocity automatically drops by abouthalf. This reduced velocity improves diffusion filtering in theconnecting channels shown in FIGS. 2 and 3. At 119 (FIGS. 2 and 3) asmall particle (shown much enlarged) is lodged against a connectingchannel 1 13; this particle, which was removed from the flow stream bydiffusion, is held-to the channel wall by van der Waals force.

It should be noted that connecting channels such as 113 (FIG. 3) conductfluid to the successive filtration stage by two routes. Thus, even ifthe left (or right) portion of the connecting channel 113 should becomeobstructed,'the fluid alwayshas an alternativepath to the next stage. Ifa laminar flow channel shouldclog, the connecting channel of theprevious stage then provides analternate path around the clogged laminarflow channel.

With reference to FIG. 3, if the direction of flow in laminar flowchannel 112 is reversed (so as to be in directions opposite to the shownflow arrows) an impact target surface is formed adjacent point whereconnecting channel 104 has its juncture with laminar flow channel 112.The filtration structure thus has impaction filtering occurring adjacentpoint 105 instead of 116. Flow would enter the laminar flow channel 112adjacent point 116 which would now be at the upstream end of the laminarflow channel. Particle accumulation 118 and lodged particle 119 would,of course, then occur in channel 104. It is thus clear that with thefiltration structure 110, the direction of flow has no effect onfiltering efficiency.

It should be understood that when the flow direction is opposite to theshown arrows, the connecting channel associated with the filtrationstructure 110 is no longer channel 113 because the connecting channelmust be located at the downstream end of laminar flow channel 112. Thus,the connecting channel for filtration structure 110 would be channel104, which extends between points 106 and 206. Throughout thisspecification, the term connecting channel shall always refer to achannel located at the downstream end of a laminar flow channelextending to the upstream end or between the upstream ends of successivelaminar flow channels if there are successive laminar flow channels. Ifnot, the connecting channel is connected to exit means. The termconnecting passage has a like meaning but applies to channels which havebeen closed to form passages.

The impact target surface adjacent point 116 shown in FIG. 3 is but onetype of impact target surface which can be used with the invention.Connecting channel 113 need not be formed from an arc of a circle asshown in FIGS. 2 and 3; connecting channel 113 and the impact targetsurface formed thereby will function equally well if connecting channel113 has a straight line portion intersecting channel 112. Operation is,of course, identical with a straight connecting channel and will not bedescribed further.

Another type of impact target surface is shown in FIG. 4. There laminarflow channel 61 is terminated at its downstream end'by connectingchannel 63 which changes direction as it joins channel 61 to form apointed junction area 65. An impact target surface is formed adjacentpoint 67 by the junction, and an accumulation of particles 69 is shownon the impact target surface. The direction of fluid flow through thechannels is indicated by flow arrows. Fluid flows from the upstream endof laminar flow channel 61 along channel 61 until it strikes an impacttarget surface adjacent point 67 where particles are removed and theflow divided to right and left into connecting channel 63. In theconnecting channel, diffusion filtering occurs and additional particlesare removed.

If the direction of flow indicated by the flow arrows in FIG. 4 isreversed, the filter structure of FIG. 4 functions equally well. Ifreversed, fluid in laminar flow channel 61 is directed toward point 60and the impact target surface is formed by connecting channel 62adjacent point 60. The fact that fluid flowing in the structure of FIG.4 must undergo a sharper turn at the impact target surface should makethe filtration slightly more efficient than the essentially right angleturn at the impact target surface adjacent point 116 in FIG. 3. Thestructure of FIG. 3, however, is better suited for applicationsrequiring compactness. 7

Still another type of impact target surface is illustrated in FIG. 5.The direction of fluid flow in FIG. is indicated by flow arrows. Therelaminar flow channel 71 intersects connecting channel 73 to form forkjunction 75. Fluid passing down laminar flow channel 71 collides with animpact target surface adjacent point 77 formed by the inner surface ofconnecting channel 73. Particles colliding with the impact targetsurface build up a particle accumulation 79. Fluid flow divides to rightand left as it enters connecting channel 73. Additional particles areremoved by diffusion in channel 73. The filtration structure of FIG. 5is equally operational if the direction of fluid flow is reversed. Whenfluid flow is reversed, the impact target surface, of course, is locatedadjacent point 70 instead of at junction 75, and the channel 74 becomesthe connecting channel.

With each of the impact target surface configurations illustrated inFIGS. 3-5 the connecting channels serve identical purposes. They reducethe velocity of fluid leaving the laminar flow channels to minimizeturbulence and promote diffusion filtering, and they guide fluid to thelaminar flow channels associated with a successive filtration stage.Referring to FIGS. 4 and 5, it is presumed that a closure meanscooperates with the shown channels to form closed passages when thesystem is in operation. The closure means is not shown in FIGS. 4 or 5.

Removal means, for this invention, need not be an impact target surface.For example, if the filtration method selected were interception, anarrow rod, fiber, or bead could be placed in the flow stream as removalmeans. If the gravity settling method were used, the removal means wouldconstitute achannel or channels where flow could gradually slow down andparticles settle to the channel walls. If the centrifugal filtrationmethod were utilized, the removal means might be curved or spiraledchannels leading from the downstream ends of laminar flow channels tothe conn'ecting channels. r v

If diffusion filtering were the filtration method to be adopted, theremoval means might comprise a channel or system of channels where flowvelocity is greatly reduced so as to permit Brownian movement to betterfunction as a filtering agent. After filtration has thus been obtained,fluid would conducted by the connecting channels of the invention to thenext filtration stage.

A filtration structure, such as shown in FIGS. 4-6 can be usedefficiently for filtering without being embodied in the precise channelsystems shown in FIGS. 2 or 7. For example, a plurality of structurescould simply be placed in series connection to form a chain ofsuccessive filtration structures with the two ends of each connectingchannel converging to lead to the upstream end of the laminar flowchannel of a filtration structure forming the successive stage.

The intricate combination of filter channels shown on washer 25 in FIG.2 can be analyzed as a plurality of individual filtration structureslike the one shown in part in FIG. 3. Two such filtration structuresmake up each stage of the filter of FIG. 2. Assuming flow in FIG. 2 tobe from the outer edge 58 of the washer 25 toward the core 30, thewasher has 10 filtration stages, each stage having 2 filter structures.Individual filtration structures are designated by numbers belonging tothe sequence 100, 110, 120, 200, 210, 220, 230 280, 290. In explainingthe relationship between individual filtration structures and successivestages of the filter, I shall first presume that fluid flow originatesat the outer edge 58 of the filter washer 25 and proceeds inward alongthe channels toward the core 30.

The first filtration stage, as counted from the outer edge 58 of thewasher 25, contains two filtration structures, namely structures 100 and200. To reach these filter structures, the fluid at the outer edge 58enters the washer through openings 101 and 201 which lead to laminarflow channels 102 and 202, respectively, associated with filtrationstructures 100 and 200, respectively. When flow is from the outer edge58 toward the core 30, openings 101 and 201 provide entrance means forthe fluid. As is clear after examination of FIG. 2, if fluid flow werefrom the core 30 to the outer edge 58, openings 101 and 201 wouldrepresent part of the exit means for the filtered fluid.

FIG. 6 is an edge view of three filter washers stacked one on top ofanother. The washer 26 is shown below and in contact with washer 25,permitting washer 25 to provide closure means for the channels of washer26. The channels of washer 26 are thereby transformed into closedpassages. The openings 101 and 201 are clearly shown, and it should benotedthat the orientation of individual washers is not a factor. Theopenings 101 and 201 need not be aligned with other such openings orhave any particular angular separation from other openings. This greatlyeases assembly of the washer into a filter washer stack 24 (FIG. 1). InFIG. 1 the plurality of openings 101 and 201 are shown randomly locatedabout the outer periphery of washer stack 24.

Referring now to FIG. 2, after entering openings 101 and 201 fluidfollows laminar flow channels 102 and 202, respectively, until itreaches impact target surfaces located adjacent points 106 and 206,where impaction filtration (occurs. The fluid from each laminar flowchannel then divides to left and right and follows connecting channels103 and 203, respectively. Connecting channel103 extends from point 105to 205 and intersects laminar flow channel 102; connecting channel 203extends from point 205 to 105 and intersects laminar flow channel 202.As has already been stated with respect to FIGS. 3-5, the flow velocityin connecting channels is reduced to approximately one half the velocityin the previous laminar flow channel, viz 102 or 202 (FIG. 2).

Directing attention now to filtration structure 100, fluid leaving theimpact target surface adjacent point 106 flows along connecting channel103. A first portion of the fluid travels along channel 103 toward point105. A second portion travels along channel 103 toward point 205 locatedat the opposite edge of the washer. Connecting channel 103 thus conductsthe fluid to the laminar flow channels 1 12 and 212 of filtrationstructures 110 and 210, respectively, which make up the secondfiltration stage. As filtration structure 100 conducts fluid to points105 and 205 via connecting channel 103, filtration structure 200conducts fluid to points 105 and 205 via connecting channel 203. Atpoints 105 and 205 pairs of flow streams converge and recombine prior toentering the laminar flow channels 112 and 212 of the second filtrationstage. After entering those channels, fluid velocity increases to avalue approximately twice that of the velocity in channels 103 and 203.In short, the flow velocity in laminar flow channels 112 and 212 issubstantially equal to that in laminar flow channels 102 and 202.

Fluid flows along laminar flow channels 112 and 212 and on reachingimpact target surfaces located at points 116 and 216, respectively,undergoes impaction filtration. After impaction, the flow divides toleft and right in each connecting channel and the fluid velocity dropsto approximately half the velocity in laminar flow channels 112 and 212.The flow from laminar flow channel 112 separates to follow connectingchannel 113 to its ends at points 115 and 215. The flow leaving laminarflow channel 212 also separates as it enters connecting channel 213 andflows to left and right until reaching the ends of connecting channel213 at points and 215. As flow reaches points 115-and 215, divided flowstreams recombine and fluid is ready to enter the third filtrationstage. The third filtration stage consists of filtration structures and220. Fluid enters laminar flow channels 122 and 222, respectively, ofthe third stage, at an increased velocity which is approximately equalto the flow velocity in laminar flow channels 112 and 212. At the end oflaminar flow channels 122 and 222, fluid encounters impact targetsurfaces located adjacent points 126 and 226, respectively, whichcollect contaminant particles. After impaction flow is divided equallyto left and right along connecting channels 123 and 223 of structures120 and 220, respectively, of the third stage, and the velocity thereinis reduced by half. The connecting channels conduct fluid to the fourthfiltration stage which consists of filtration structures 130 and 230.

Fluid passing through structures 130. and 230 undergoes the sameimpaction filtration process as has been described for the first threefiltration stages. At impact target surfaces located adjacent points 136and 236, the flow, as before, divides to follow connecting channels 133and 233, respectively, and flow velocity is reduced.

Since the operation of the filtration structures of each filtrationstage is essentially identical, the detailed operation of stages5,6,7,8, and 9 will not be described in detail; should it be desirableto trace the fluid flow through the system of channels forming thesestages, no difficulties should arise. Corresponding elements of eachfiltration structure are designated by similar num bers; for example,each filtration structure has a number, 100 or greater, which is aninteger multiple of 10; each laminar flow channel has a number whosefinal digit is 2; each connecting channel has a number whose final digitis 3.

As fluid flow passing across filter washer 25 reaches the finalfiltration stage, namely the tenth stage, it flows along laminar flowchannels 192 and 292 of filtration structures and 290, respectively.After particles are removed at impact target surfaces adjacent points196 and 296, flow continues along connecting channels 193 and 293,respective y, and leaves the washer by exit means provided by openings199 and 299, respectively. Flow has now reached the central core 30 ofthe washer 25.

Referring now to FIG. 1, when the many filter washers such as washer 25,are fully assembled and aligned in washer stack 24 and the filterassembly 10 fully assembled, pressurized fluid enters inlet passage 20and flows into reservoir 22. From the reservoir 22, fluid enters themany small openings such as 101, 201 in the filter stack 24 which areidentical to those shown at 101, and201 in FIG. 2. Fluid passes acrossthe many filter washer plates by following the intricate channel system27 thereon and ultimately reaches washer stack core 32 (FIG. 1). Thefluid then flows along washer stack core 32 and passes through uppercollar 40 and into outlet passage 42. The fluid has now been fullyfiltered.

Up to this point the description of filtration action in filter washer25 has assumed that the direction of fluid flow is from the outer edge58 toward the central core 30. As stated earlier, the washer system 27is equally operational with flow originating at the central core 30 andpassing across the washer plate 25 to the outer edge 58. One difference,however, does exist between center-to-edge and edge-to-center filtering.If the flow originates at the outer edge 58 and flows toward the centercore 30, it passes through ten filter stages. If the flow originates atthe center core 30 and moves toward the outer edge 58, it passes throughnine stages. The difference occurs at filter structures 100 and 200.When flow is toward the outer edge 58, these two filter structures haveno impact target surfaces to perform filtration operations, and hencethese two structures do not form an operational filter stage when flowis from core 30 toward the outer edge 58.

In operation, when flow is from the core 30 toward the outer edge 58,openings 199 and 299 and channels 193 and 293, adjacent the core,provide entrance means for fluid and conduct the fluid to the firstfiltration stage (as measured from the core 30). The fluid, afterentering openings 199 and 299, flows along channels 193 and 293,respectively, until'it reaches laminar flow channels 192 and 292,respectively, of the first filtration stage. It should particularly benoted that the impact target surfaces formerly provided adjacent points196 and 296 when flow was from the outer edge 58 toward the core 30 nolonger serve as impact target surfaces No impaction occurs at surfacesadjacent points 196 and 296. Filtration structures 190 and 290, instead,have their impact target surfaces adjacent points 185 and 285. Afterimpaction filtering occurs at the first-stage impact target surfacesadjacent points 185 and 285 the fluid enters connecting channels 194 and294 of the first filtration stage. Channel 194 extends between points186 and 286 and intersects the downstream end of laminar flow channel192; channel 294 extends between points 286 and 186 and intersectslaminar flow channel 292. It should be noted that filtration structures190 and 290 utilize connecting channels 194 and 294, respectively, whenflow is from core-toedge, and connecting channels 193 and 293 when flowis from edge-to-core. The connecting channel is always located at thedownstream end of the laminar flow channel. The flow divides to left andright as it leaves laminar flow channels 192 and 292, and velocity offlow is reduced to approximately half the velocity in laminar flowchannels 192 and 292. Fluid leaving point 185 flows along connectingchannel 194 which extends between points 286 and 186. Simultaneously,fluid leaving point 285 flows through channel 294 to reach points 286and 186. At points 286 and 186 pairs of reduced velocity fluid streamscombine and enter the laminar flow channels of the second filtrationstage, as counted from the core. This second filtration stage consistsof filtration structures 180 and 280.

Fluid flows along laminar flow channels 182 and 282 of structures 180and 280, respectively, becoming laminar prior to reaching impact targetsurfaces located adjacent points 175 and 275, respectively. Fluid thenenters the connecting channels 184 and 284 associated with the secondfiltration stage, as measured from the core. Connecting channel 184extends between points 176 and 276 and intersects the downstream end oflaminar flow channel 182; connecting channel 284 extends between points276 and 176 and intersects the downstream end of laminar flow channel282. In these connecting channels fluid velocity is approximately onehalf that in laminar flow channels 182 and 282. As pairs of flow streamsconverge at points 176 and 276, they combine to enter the thirdfiltration stage (as measured from the core), which consists offiltration structures 170 and 270. In this third stage, the filtrationprocess is identical to that described in the first and second stages.At every filtration structure through which fluid passes in travelingfrom the core 30 to the outer edge 58, it undergoes the same filtrationprocess which has already been described in detail for the first twostages. It should be understood that when fluid flow is from the core 30to the edge 58, the impact target surfaces are not located at the sameend of the laminar flow channel as when flow is from the edge 58 to thecore 30; the impact target surfaces are then located at the opposite endof the laminar flow channels at points such as 165, 265, 155, 255,145,245, etc.

Ultimately, the fluid reaches the final filtration stage containingstructures 110 and 210 and after colliding with impact target surfacesadjacent points and 205 enters connecting channels 114 and 214,respectively, which conduct the fluid to channels 102 and 202. Channels102 and 202 and openings 101 and 201, collectively, provide exit meansfor the fluid when the flow direction is from the core 30 to the outeredge 58.

When the flat unchanneled blank surface of a second washer or some otherclosure means is compressed against the channel system of a washer, thechannels become closed on all sides to form passages which can containthe flowing fluid. To operate effectively, the washer channels must, ofcourse, be closed to form passages.

It has been found that space on the washer surface is greatly conservedwhen portions of connecting channels are formed as concentric circularchannels. Accordingly, arcs of the connecting channels have been madeconcentric whenever possible. Straight line channels have been used tojoin circular portions where convenient to offset. one laminar flowchannel from another. This offsetting permits one to have a large numberof laminar flow channels of considerable length in a small surface area.

It should be understood that when fluid flows from the core 30 towardthe outer edge 58, the fluid is supplied to the filter assembly 10(FIG. 1) through passage 42. Fluid is thus directed into the stack core32 and enters the openings 199, 299 (FIG. 2) of individual washers.Fluid leaving the washers enters the reservoir 22 (FIG. 1) and thenleaves the filter assembly 10 by passage 20.

A second embodiment of the invention is shown in FIG. 7. The filterchannel system of FIG. 7 is equally operational whether flow is from theouter edge 302 of washer 300 toward the core 390 or visa versa. Thestructural characteristics and operation of the embodiment of theinvention shown in FIG. 7 will now be explained in detail with theassumption that fluid flow is from the outer edge 302 toward the core390.

The washer 300 shown in FIG. 7 can be used in the washer stack 24 of thefilter assembly 10 shown in FIG.

1. Fluid is, of course, supplied by the filter assembly 10' toindividual washers in the washer stack 24 in the same I manner asalready described for the channel system of FIG. 2.

Plane 8-8 is shown dividing the washer plate of FIG. 7 into twosubstantially equivalent halves. The channel system shown in the upperhalf of FIG. 7 is identical to that shown in the lower half. To simplifythe description of this embodiment, only the lower half of the washerplate will be described in detail, since structural characteristics andoperation of the upper half are identical.

In FIG. 8 the lower half of the washer 300 of FIG. 7 is shown greatlyenlarged. A plurality of openings such as 310, 312, 314, 316, 318, and319 are positioned at spaced intervals along the outer, edge 302 of thelower half of washer 300. It will be observed that the upper half of thewasher 300 has a plurality of like openings spaced along the outer edge.(FIG. 7).

The openings in the outer edge 302 of washer 300 (FIG. 8) supplyentrance means for fluid flowing into the filter washer 300 when flow isdirected from the outer edge 302 toward the core 390. Fluid entering theopenings flows along individual laminar flow channels such as 320, 322,324, 326, 32 8, or 329. To illustrate, fluid entering opening 314 flowsalong laminarflow channel 324. Each of these laminar'flow channels aremade of sufficient length to establish laminar fluid flow before thefluid reaches the downstream end of the laminar flow channel. As statedearlier, to obtain laminar flow, the wallsshould be reasonably smoothand straight and the channel of appropriate length to reduce turbulence.

Since all the filtration structures within the lower half of the washerof FIG. 8 are similar, I shall henceforth concentrate my descriptionupon the fluid entering openings 312, 314, and 316 and the filtrationstructures associated with those openings. When one understands thebehavior of fluid entering the washer by these openings, the operationof the entire filter washer 300 is easily understood.

Fluid flowing along laminar flow channel 322 reaches connecting channel330which extends from point 331 to point 333 and intersects thedownstream end of laminar flow channel 322. At the intersection betweenlaminar flow channel 322 and connecting channel 330, an impact targetsurface is formed adjacent point 334. Fluid reaching the downstream endof laminar flow channel 322 has laminar flow characteristics, andparticles carried by the fluid are traveling at the velocity of thefluid. As fluid reaches the inter section with connecting channel 330,it is forced to divide to left and right to follow connecting channel330. Since the particles carried by the fluid have greater mass then thefluid molecules, their momentum tends to carry them straight aheadinstead of permitting them to turn to follow channel 330. Particlescolliding with the impact target surface adjacent point 334 adhere to itand are removed from the fluid. As the fluid divides on enteringconnecting channel 330, its velocity is reduced to approximately halfthe velocity found in laminar flow channel 322. The combinationconsisting of laminar flow channel 322, connecting channel 330 with animpact target surface adjacent point 334, and closure means (not shown)collectively form filtration structure 332 which is similar in form andpurpose to the filtration structures making up the embodiment of I6 theinvention shown in FIG. 2. It should be understood that the structure332 requires closure means for the channels in order to be an operativestructure.

As fluid enters laminar flow channel 322, it is simultaneously enteringlaminar flow channels 324 and 326 through openings 314 and 316,respectively. Fluid reaching the downstream end of laminar flow channel324 divides to right and left along connecting channel 335 which extendsbetween points 333 and 336. At the inter-section between. connectingchannel 335 and laminar flow channel 324, an impact target surface ifformed adjacent point 337. Similarly, connecting channel 338 extendsbetween points 336 and 339. At the intersection of connecting channel338 with laminar flow channel 326 an impact target surface is formedadjacent point 340.

The fluid leaving laminar flow channels 324 and 326 divides to left andright along connecting channels 335 and 338, respectively. In eachinstance, the velocity of fluid flow in the connecting channels is halfthe velocity in the laminar flow channels. As fluid reaches the ends oflaminar flow channels 324 and 326, particles'collide with impacttargetsurfaces located adjacent points 337 and 340, respectively, andthese colliding particles are removed from the'fluid. Laminar flowchannel 324, a connecting channel 335 with an impact target surfaceadjacent point 337, and appropriate closure means, collectively formfiltrationstructure 341.

Another filtration structure 343 is formed by laminar flow channel 326,connecting channel 338 with an impact target surface adjacent point 340,and appropriate closure means. If the filter washer plate is examined asa whole, it will be noted that the entire filter channel system consistsof a plurality of like filtration structures.

Connecting channels 330, 335, and 338 have their ends connected to forman arc of a circle; this are is part of a circular channel formed byfiltration structures which have the ends of their connecting channelsjoined together. The plurality of filtration structures whose connectingchannels form arcs of the same circle are to be considered as belongingto the same stage. When flow is from the outer edge 302 toward the core390 the structures whose connecting channels form the circular channelof largest diameter belong to the first filtration stage. Any fluidpassing across the filter washer plate from the outer edge 302 willundergo a first filtration in a filtrationstructure belonging to thisfirst filtration stage.

It is not essential that the connecting channels be of any specificlength. The connecting channels have several purposes: they conductfluid from the impact target surface of a filtration structure to thelaminar flow channels associated with successive filtration structures;they provide a channel wherein velocity is reduced to better facilitatediffusion filtering; in addition, if one connecting channel becomesobstructed, flow will not cease since fluid flows to right and left ineach connecting channel thus providing an alternative path.

Fluid from connecting channels of filtration structures 332 and 341 ofthe first filtration stage converges at point 333 to enter the secondfiltration stage. Simultaneously, fluid from filtration structures 341and 343 of the first filtration stage converges at point 336 to 1 7enter the second filtration stage. This converging behavior occurs atthe ends of each connecting channel on washer 300.

Fluid streams converging at point 333 enter laminar flow channel 342.Fluid streams converging at point 336 enter laminar flow channel 344.After laminar flow is established, the fluid undergoes impactionfiltration at impact target surfaces. Flow along laminar flow channel342 is filtered at an impact target surface adjacent point 345 which isformed by the intersection of connecting channel 346 with laminar flowchannel 342. Connecting channel 346 extends between points 347 and 348.Similarly flow proceeding along laminar flow channel 344 encounters animpact target surface located adjacent point 349 which is formed by theintersection of connecting channel 350 with laminar flow channel 344.Connecting channel 350 extends between point 348 and 351. All filtrationstructures having their connecting channels coincident with the circularchannel formed in part by the arcs of connecting channels 346 and 350are in the second filtration stage.

As the fluid leaves the downstream end of laminar flow channels 342 and344, it divides to right and left along connecting channels 346 and 350,respectively, and fluid velocity in the connecting channels is reducedto approximately half the velocity in the laminar flow channels. 'Fluidflow from connecting channels 346 and 350 converges at point 348.

Fluid converging on point 348 enters laminar flow channel 352 andattains laminar flow before reaching the downstream end of the channel.As the fluid leaves laminar flow channel 352 contaminant particlescollide with an impact target surface located adjacent point 353 whichis formed by the intersection of connecting channel 354 with laminarflow channel 352. Fluid leaving laminar flow channel 352 divides to leftand right along connecting channel 354 which extends between points 355and 356. Laminar flow channel 352 is a part of filtration structure 357which is in the third filtration stage.

It should be understood that fluid entering the many remaining openingsaround the outer edge 302 of the washer such as 310, 318, and 319receives the same filtration action already described for fluid enteringthe sector of the washer containing openings 312, 314, and 316. Thefiltration process has been described in detail for fluid flow throughportions of the first three stages of the filter. To avoid needlessrepetition, the details of filtration in the fourth, fifth, and sixthstage will not be intricately described since they are similar tofiltration in the first three stages. A slight change in behavior occursin the fifth, sixth, and seventh stages, but this will be describedhereafter.

As fluid reaches the seventh and final filtration stage, it enterslaminar flow channels associated with that stage such as laminar flowchannel 381. After impact filtering occurs at an impact target surfacelocated adjacent point 382, fluid enters connecting channel 383 whichextends between points 384 and 385. Fluid flowing along connectingchannel 383 of the seventh stage leaves the filtration structure throughchannels 387 and 388 which lead to interior openings 389 and 391. Thechannels 387 and 388 with interior openings 389 and 391, collectively,comprise exit means for the fluid leaving the washer. Naturally, otherchannels and interior openings around the periphery of the central core390, such as channels 394 and 395 and openings 392 and 393, though notdescribed in detail, also constitute exit means when fluid flow is fromthe outer edge 302 toward the core 390.

As fluid leaves the final filtration stage of the washer 300, it entersthe stack core 24 (FIG. 1) and then leaves the filter assembly bypassage 42.

As stated earlier, as one encounters the fifth filtration stage of thewasher 300 (FIG. 8) some slight differences in fluid flow occur. Fluidleaving the connecting channels of the fourth filtration stage encounterfewer laminar flow channels in the fifth stage than were present instages one through four. The number of laminar flow channels in thefifth filtration stage has deliberately been reduced because thisincreases the velocity of fluid entering the laminar flow channels ofthe fifth stage. As velocity is increased, even smaller particles can beremoved by impaction filtering. It should be understood that thisreduced number of laminar flow channels need not have been incorporatedin this filter washer and that the number of laminar flow channels inthe fifth and later stages could have been kept at a number which wouldnot have introduced a higher velocity of flow. In addition, thereduction of the number of laminar flow channels could have occurred inthe fourth stage, the sixth stage, etc., depending on filtrationrequirements. 1

The filtration process occurring with filter washer 300 will now bedescribed in detail when fluid flow originates at the core 390 and flowsacross the washer toward the outer edge 302. In such a case, fluidenters the filter assembly 10 (FIG. 1) by passage 42 which leads towasher stack core 32. Fluid then has reached the washer 300 FIGS. 7 and8).

Fluid flow originating at the central core 390 (FIG. 8) enters interioropenings such as 389, 391, 392, and 393. These interior openings provideentrance means for'the fluid when fluid flow originates at the centralcore. Fluid next enters individual filtration structures and flows alongthe corresponding laminar flow channels of each structure until itreaches the downstream end of each channel. For example, fluid enteringinterior opening 389 flows along laminar flow channel 387 of filtrationstructure 407; fluid entering interior opening 391 flows along laminarflow channel 388 of filtration structure 408. By the time fluid reachesthe downstream end of the individual laminar flow channels, the fluidhas attained laminar flow. Since the individual construction andoperation of each filtration structure is essentially like that of allothers, the operation of the filter will only be described in detail forthe filter structure 407 and 408 in the first filtration stage, ascounted from the core 390. As flow reaches the downstream end of laminarflow channels 387 and 388, impact filtering occurs at impact targetsurfaces located adjacent points 384 and 385, respectively. Flow fromstructure 407 then divides to left and right along connecting channel396 which extends from point 382 to point 397. Simultaneously, fluidflow leaving the downstream end of laminar flow channel 388 offiltration structure 408 divides to left and right along connectingchannel 409 which extends between points 382 and 410.

Portions of the fluid flow from connecting channels 396 and 409 convergeat point 382 to enter laminar flow channel 381 of the second filtrationstage. As the fluid reaches the downstream end of channel 381, itundergoes impaction filtration at an impact target surface adjacentpoint 411 and then divides to left and right along connecting channel412 which extends from point 413 to point 414. Laminar flow channel 381and connecting channel 412 with its impact target surface along withappropriate closure means form filtration structure 415.

It should be understood that fluid flow continues from the central core390 toward the outer edge 302 of the filter by passing throughsuccessive filtration structures associated with successive filtrationstages until ultimately the flow reaches the final filtration stage.When flow is from the central core 390 toward the outer edge 302, afinal filtration stage is composed of filtration structures such asstructures 420 and 422. Fluid reaching structure 420 flows along laminarflow channel 342 and undergoes impaction filtration at an impactv targetsurface located adjacent point 333. It then divides to leftand rightalong connecting channel 424 which extends between points 334 and 337.Fluid from laminar flow channel 344 of structure 422 divides to left andright as it enters connecting channel 425 extending between points 337and 340.

At point 337, two streams of fluid converge to enter channel 324. Fluidleaves the washer through opening 314. It should be understood thatstructures 420 and 422 were chosen as typical of the many structures inthe final filtration stage and that the many like structures perform ananalogous filtering operation. When flow is from the central core 390 tothe outer edge 302, outer channels such as channels 322, 324, 326, etc.,connecting with-openings 312, 314, 316 and the like provide exit meansfor the fluid flow. Fluid next enters V reservoir 22 (FIG. 1) and thenflows through passage 20 to leave the filter assembly 10.

It should be noted that the impact target surface for each filtrationstructure (FIGS. 2, and 4-8) is always located at the downstream end of.the laminar .flow channel associated with the structure. Thus,depending upon the direction of flow, the impact target surface of agiven filtration structure may be at either end of the laminar flowchannel.

It should be understood that fluid flowing through the connectingchannels in the filter washer shown in FIG. 7 and 8 is traveling at avelocity less than that present in laminar flow channels. This loweredvelocity results in improved diffusion filtering in the connectingchannels. In this way, many small particles which would otherwise not beremoved can be eliminated from the fluid during its travel through theconnecting channels.

The embodiments shown in FIGS. 2, 7, and 8 utilize both impactionfiltering, and diffusion filtering. In each embodiment, fluid velocityis halved as it enters connecting channels; this reduction facilitatesdiffusion filtering, which operates best at lowered velocities.

FIG. 9 illustrates a channel variation which can be utilized with thechannel washer system of FIGS. 2 or 7. The filter washer 452, shown inpart in FIG. 9, is illustrated with two filtration stages thereon. Thefiltration structure 455 is a part of the first filtration stage. Itshould be noted that the effective diameter of all channels in the firstfiltration stage is constant. The second filtration stage, whichcontains filtration structures 465 and 475, has the diameter of itschannels reduced. This reduction in channel diameter has been foundhelpful to increase the flow velocity from one filtration stage of afilter washer to the next, thereby permitting smaller particles to beremoved at successive stages. In addition, it has been foundthat whereit is necessary to coalesce fine droplets of mist or oil vapor it ishelpful to utilize at least one narrowed diameter channel filtrationstage to better coalesce the droplets and thus remove them from thefluid.

The extent to which channels of a successive filtration stage shouldhave their effective diameter reduced depends on the applicationintended for the filter. Or-

dinarily, one would reduce the effective diameter of a successivefiltration stage by at least a factor of 2 over the preceeding stage.This would make the channels of the successive stage half the effectivediameter of the channels of the preceeding stage. Seldom would one wishto decrease the successive filtration stage channel diameters by morethan a factor of 10. It should be understood that reducing the channeldiameter results in increased velocity, but naturally the volume offluid passing through the reduced channel diameter filtration'stage issomewhat reduced. The original volume of fluid can be restored byincreasing the number of filtration structures in the filtration stageswhere channel diameter has been reduced.

The channel diameter variation principle illustrated in FIG. 9 can beutilized in the channel system shown in FIGS. 2 or 8. If desired, theeffective diameter of channels can decrease with each successivefiltration stage. Alternatively, the filter system can contain a set offiltration stages havinga fixed effective diameter for all channelswithin that set, and additional sets of successive stages with adifferent effective diameter for each set can be provided as required.

Individual washers, whether embodying the design of FIG. 2 or 7, can befabricated from a variety of different materials depending upon theapplication intended. Possible materials include plastic, glass,ceramics, or almost any metal or alloy thereof. Of the metal group,stainless steel or-aluminum has been found to function well. If a hightemperature application is planned, it is advisable to choose a materialwhich has a relatively high melting point. Stainless steel filterwashers can operate efficiently in temperatures as high as 1,000 C.Naturally, the other components making up the filter assembly 10 shownin FIG. 1 must be made of material capable of withstanding the same hightemperatures. The channel system can be formed in the filter washers ina variety of ways such as etching or stamping.

It has been found that a stacked washer filter is an excellent filterfor applications where large pressures are involved. The sturdy filterwasher stack used with the invention can withstand pressures as high as5,000 psi without danger of collapse. Naturally, the casing should havea compatible strength. The device is well adapted to be connected tostandard factory air pressure supply sources which ordinarily are in the-100 psi range. Typically a pressure drop of approximately 20 psi occursacross the filter when it is in operation.

Another advantage of this invention is that when it ultimately becomessaturated with particles, it is easily cleaned. To clean the individualfilter washers, one disconnects the casing 14 from the head 12 (FIG. 1)and then withdraws the washer stack 24 from the casing 14. One thenunthreads nut 48, and the individual washers can be removed from rod 44for cleaning. Emersion in an appropriate cleaning solution, scrubbing,ultrasonic cleaning or other appropriate means will remove theaccumulated surface particles on the filter washers. If the filter unitis used to purify gases at high temperatures, such as l000 C, the filterwashers become so hot that solid organic dirt particles lodged thereinliterally disintegrate. At this temperature solid organic particles areconverted to a gaseous state. In effect, the filter washer stack 24, atsuch a temperature, becomes a self-cleaning oven.

When reassembling the washer stack 24, no orientation problems, asidefrom vertical alignment, exist. The positioning of openings such as 101and 102 (FIG. 2) along the outer periphery requires absolutely noattention. This fact greatly diminishes the toil of reassembling thewasher stack.

The size of individual washers can be varied according to need. It hasbeen found that circular washers having an outer diameter ofapproximately 1.625 inches and an inner diameter of approximately 0.75inches function well for most filter applications. Ordinarily,individual washers are quite thin, i.e., 0.005 inch thick, but this isvariable depending on the application. Typically, individual channelshave widths ranging between 0.004 and 0.010 inch, although this range isnot compulsory. The depth of an individual channel is commonly about0.0025 inches. In determining the width and depth dimensions ofindividual channels, it is helpful to first know the sizes ofcontaminant particles which are to be removed. The smallest channeldimension (either width or depth) should be at least times the diameterof the largest expected particle. If channels are made smaller, the riskof channel clogging is greatly increased. If one expects occasionalparticles of diameter equal to or greater than one tenth of the smallestchannel dimension, it would be prudent to install a prefilter to removethese large particles before sending the fluid through the channels ofmy filter invention.

In the embodiments shown in FIGS. 2 and 7, the width and depth ofindividual channels is constant throughout the filter washer. Ifdesirable, it is possible to vary the width or depth of the individualchannels from one stage of the washer to the next. For example, thefirst three stages of the filter washer shown in FIG. 2 could havechannels widths of 0.010 inch and the remaining stages could havechannel widths of 0.004 inch. With such variation, the more coarseparticles would be removed by the first three stages and finer materialsby the final stages where the channels are of smaller width. It shouldbe understood that a decrease in the width of a laminar flow channelpermits a decrease in the length of the laminar flow channel withoutadversely affecting laminar flow. By such a decrease in width, a greaternumber of filtration stages can be placed in a given area.

If desired, it is possible to use a washer stack consisting of a mixtureof washers. The stack could contain washers of the type described inFIG. 2 and also washers of the type shown in FIG. 7. A single washerdesign is not essential to the filter assembly 10 to obtain efficientfiltration.

The number of required filtration stages per washer needed for aparticular application is easily computed using the followingrelationship:

Number l i where E the required efficiency of a filter having therequired number of stages and E, the efficiency of an individualfiltration stage. Efficiency is the ratio of particles removed from thefluid during filtration to particles in the fluid prior to filtration.

While I have described several preferred embodiments of the presentinvention, it should be understood that various changes, adaptions andmodifications may be made therein within departing from the spirit ofthe invention and the scope of the appended claims.

What is claimed is:

1. A fluid flow filter for removing contaminant particles dispersed in afluid comprising:

a filter body a fluid flow passage for conducting fluid through saidbody, said fluid flow passage including a substantially straight smoothsection of sufficient lengthto permit fluid flowing therealong todevelop laminar flow characteristics, said substantially straight smoothsection comprising a laminar flow section; and

particle removal means disposed at the downstream end of said laminarflow section for interacting with the laminar flowing fluid and removingdispersed particles from said fluid.

2. The combination according to claim 1 wherein said body has aplurality of fluid flow passages, and each of said fluid flow passageshas a plurality of successive laminar flow sections and particle removalmeans, one of said particle removal means located at the downstream endof each successive laminar flow section thereby forming successivefiltration stages.

3. The combination according to claim 2 wherein said fluid flow passagesfurther include a plurality of connecting segments, wherein eachconnecting segment intersects the downstream end of a given laminar flowsection and extends between the upstream ends of at least two successivelaminar flow sections when there are laminar flow sections successive tothe given laminar flow passage.

4. A fluid flow filter for removing contaminant particles dispersed in afluid comprising:

a filter body a plurality of fluid passages for conducting fluid throughsaid body, each fluid flow passage having a plurality of successivesmooth sections of sufficient length to permit fluid flowing therealongto develop laminar flow characteristics forming successive filterstages, said smooth sections comprising laminar flow sections, and aplurality of connecting segments, wherein each connecting segmentintersects the downstream end of a given laminar flow section andextends between the upstream ends of at least two successive laminarflow sections where there are laminar flow sections successive to thegiven laminar flow sections, and

wherein the effective stage diameter of at least one filter stage isdifferent from the effective stage diameter of the preceding filterstage; and

particle removal means disposed at the downstream ends of said laminarflow sections for interacting with the laminar flowing fluid and forremoving dispersed particles from said fluid.

5. The combination according to claim 4 wherein the effective diameterof each laminar flow section in at least one successive filtration stageis smaller than the effective diameter of each laminar flow section inthe preceding stage, and thus each successive stage removes smallerparticles.

6. The combination according to claim 4 wherein the number of laminarflow sections and particle removal means in at least one stage differsfrom the number of laminar flow sections and particle removal means in asubsequent stage, such that fluid flow velocity can be varied from stageto stage to improve filtration efficiency. I

7. A fluid flow filter for removing contaminant particles dispersed in afluid comprising:

a filter body;

a fluid flow passage for conducting fluid through said body, each fluidflow passage having a plurality of successive smooth sections ofsufficient length to permit fluid flowing therealong to develop laminarflow characteristics forming successive stages, and

. a plurality of connecting segments, wherein each connecting segmentintersects the downstream end of a given smooth section and extendsbetween the upstream ends of at least two successive smooth sectionswherethere are successive smooth sections to a given smooth section, andwherein, the effective diameters of the individual smooth sections ofsuccessive stages are smaller than the effective diameters of theindividual smooth sections of the preceding stage and the number ofsmooth sections of said successive stages are increased so that theeffective stage diameters of the successive stages are equal; and

particle removal means disposed at the downstream ends of each of saidsmooth section for interacting with the laminar flowing fluid and forremoving dispersed particles from said fluid.

8. The combination according to claim 1 wherein said particle removalmeans is an impact target surface.

9. The combination according to claim 1 wherein said laminar flowsection has length and width dimensions such that the ratio of length toeffective diameter is not less than ten.

10. The combination according to claim 9 wherein said ratio of length toeffective diameter is between 20 and 30.

11. A filter with a plurality of successive filtration stages thereinfor purifying fluid flow comprising:

a filter body having entrance and exit means for fluid flow;

a plurality of individual fluid flow passages for conducting fluidthrough said body, said passageineluding successive substantiallystraight sections of sufficient length to permit fluid reaching thedownstream ends thereof to develop laminar flow characteristics saidstraight sections forming laminar flow sections, and a plurality ofconnect- LII ing segments in said fluid flow. passage, each connectingsegment joins the downstream end of a given laminar flow section withthe upstream ends of two laminar flow section associated with asuccessive filtration stage, when there is a successive stage, andhaving an impact target at the junction of the downstream end of thelaminar flow section and said connecting passage;

said entrance means conducting fluid to said fluid flow passages andsaid exit means conducting fluid from the final filtration stage out ofthe filter body.

12. A filter having a plurality of successive filtration stages thereinfor purifying fluid flow comprising:

a plate having entrance andexit means for fluid flow;

a plurality of individual laminar flow channels formed on said. plate,all such channels being smooth and of sufficient length to permit fluidreaching the downstream ends thereof to develop laminar flowcharacteristics;

'a plurality of connecting channels on said plate, each of saidconnecting channels intersecting the downstream end of an individuallaminar flow channel and having an impact'target surface at theintersection, each connecting channel extending to the upstream end of asuccessive laminar flow channel when a successive laminar flow channelis present;

said entrance means conducting fluid to the laminar flow channelsassociated with a first filtration stage and said exit means conductingfluid from the connecting channels associated with a final filtrationstage out of the plate; and

closure means cooperating withsaidplate to form closed passages of thechannels on said plate.

13. The combination according to claim 14 wherein each of saidconnecting channels forms an arc of a circle, connecting channels ofsuccessive stages having their arcs concentric.

14. The combination according to claim 12 wherein portions of eachconnecting channel form arcs of circles, the arc portions of theconnecting channels of successive stages being concentric.

15. The combination according to claim 12 wherein said plate is annularand said laminar flow channels are arranged radially thereon.

16. A filter with a plurality of successive filtration stages thereinfor purifying fluid flow comprising:

a filter body having entrance and exit means for fluid flow;

a plurality of individual laminar flow passages in the body saidpassages being smooth and of sufficient length to permit fluid reachingthe downstream ends thereof to develop laminar flow characteristics;

means in said body providing connection between the upstream ends of twolaminar flow passages associated with a successive filtration stage,said means intersecting the downstream end of an individual laminar flowpassage, an impact target surface being formed by the intersection ofsaid connection means with said downstream end of said laminar flowpassage; and

said entrance means conducting fluid to the laminar flow passagesassociated with a first filtration stage, and said exit means conductingfluid from the connecting passages associated with a final filtrationstage out of the said filter body.

17. A filter having a plurality of successive filtration stages thereinfor purifying fluid flow comprising:

a plate having entrance and exit means for fluid flow;

a plurality of individual laminar flow channels formed on said plate,all channels being substantially straight and of sufficient length topermit fluid reaching the downstream ends thereof to develop laminarflow characteristics;

a plurality of connecting channels on said plate, each of saidconnecting channels intersecting the downstream end of an individuallaminar flow channel and having an impact target surface at theintersection, each connecting channel extending between the upstreamends of two laminar flow channels associated with a successivefiltration stage when a successive filtration stage is present;

said entrance means conducting fluid to the laminar flow channelsassociated with a first filtration stage and said exit means conductingfluid from the connecting channels associated with a final filtrationstage out of the plate; and

closure means cooperating with said filter plate to form closed passagesof the channels on said plate.

18. A filter washer for use with a plurality of other like washerswhich, when aligned and compressed collectively form a stacked washerfilter element with a plurality of successive filtration stages on eachwasher 6 for purifying fluid flow comprising:

said washer having substantially flat first and second surfaces with acore extending therebetween and terminating at each of said surfaces,said core spaced from the outer edges of said plate;

a plurality of individual laminar flow channels of sufficient length topermit fluid reaching the downstream ends thereof to develop laminarflow characteristics, said laminar flow channels located on said firstsurface of said plate;

a plurality of connecting channels on said first surface of said plate,each of said connecting channels intersecting the downstream end of anindividual laminar flow channel and having an impact target surface atthe intersection and each connecting channel extending between theupstream ends of two laminar flow channels associated with a successivefiltration stage when a successive filtration stage is present;

means conducting fluid to the laminar flow channels associated with afirst filtration stage, and from the connecting channels associated witha final filtration stage out of the said filter washer plate; and all ofthe channels, conducting means, and impact target surfaces on said firstsurface of said plate cooperating with the flat second surface of a likeplate to form closed passages across the said plate when two like platesare aligned and compressed.

1. A fluid flow filter for removing contaminant particles dispersed in afluid comprising: a filter body a fluid flow passage for conductingfluid through said body, said fluid flow passage including asubstantially straight smooth section of sufficient length to permitfluid flowing therealong to develop laminar flow characteristics, saidsubstantially straight smooth section comprising a laminar flow section;and particle removal means disposed at the downstream end of saidlaminar flow section for interacting with the laminar flowing fluid andremoving dispersed particles from said fluid.
 2. The combinationaccording to claim 1 wherein said body has a plurality of fluid flowpassages, and each of said fluid flow passages has a plurality ofsuccessive laminar flow sections and particle removal means, one of saidparticle removal means located at the downstream end of each successivelaminar flow section thereby forming successive filtration stages. 3.The combination according to claim 2 wherein said fluid flow passagesfurther include a plurality of connecting segments, wherein eachconnecting segment intersects the downstream end of a given laminar flowsection and extends between the upstream ends of at least two successivelaminar flow sections when there are laminar flow sections successive tothe given laminar flow passage.
 4. A fluid flow filter for removingcontaminant particles dispersed in a fluid comprising: a filter body aplurality of fluid passages for conducting fluid through said body, eachfluid flow passage having a plurality of successive smooth sections ofsufficient length to permit fluid flowing therealong to develop laminarflow characteristics forming successive filter stages, said smoothsections comprising laminar flow sections, and a plurality of connectingsegments, wherein each connecting segment intersects the downstream endof a given laminar flow section and extends between the upstream ends ofat least two successive laminar flow sections where there are laminarflow sections successive to the given laminar flow sections, and whereinthe effective stage diameter of at least one filter stage is differentfrom the effective stage diameter of the preceding filter stage; andparticle removal means disposed at the downstream ends of said laminarflow sections for interacting with the laminar flowing fluid and forremovIng dispersed particles from said fluid.
 5. The combinationaccording to claim 4 wherein the effective diameter of each laminar flowsection in at least one successive filtration stage is smaller than theeffective diameter of each laminar flow section in the preceding stage,and thus each successive stage removes smaller particles.
 6. Thecombination according to claim 4 wherein the number of laminar flowsections and particle removal means in at least one stage differs fromthe number of laminar flow sections and particle removal means in asubsequent stage, such that fluid flow velocity can be varied from stageto stage to improve filtration efficiency.
 7. A fluid flow filter forremoving contaminant particles dispersed in a fluid comprising: a filterbody; a fluid flow passage for conducting fluid through said body, eachfluid flow passage having a plurality of successive smooth sections ofsufficient length to permit fluid flowing therealong to develop laminarflow characteristics forming successive stages, and a plurality ofconnecting segments, wherein each connecting segment intersects thedownstream end of a given smooth section and extends between theupstream ends of at least two successive smooth sections where there aresuccessive smooth sections to a given smooth section, and wherein, theeffective diameters of the individual smooth sections of successivestages are smaller than the effective diameters of the individual smoothsections of the preceding stage and the number of smooth sections ofsaid successive stages are increased so that the effective stagediameters of the successive stages are equal; and particle removal meansdisposed at the downstream ends of each of said smooth section forinteracting with the laminar flowing fluid and for removing dispersedparticles from said fluid.
 8. The combination according to claim 1wherein said particle removal means is an impact target surface.
 9. Thecombination according to claim 1 wherein said laminar flow section haslength and width dimensions such that the ratio of length to effectivediameter is not less than ten.
 10. The combination according to claim 9wherein said ratio of length to effective diameter is between 20 and 30.11. A filter with a plurality of successive filtration stages thereinfor purifying fluid flow comprising: a filter body having entrance andexit means for fluid flow; a plurality of individual fluid flow passagesfor conducting fluid through said body, said passage includingsuccessive substantially straight sections of sufficient length topermit fluid reaching the downstream ends thereof to develop laminarflow characteristics said straight sections forming laminar flowsections, and a plurality of connecting segments in said fluid flowpassage, each connecting segment joins the downstream end of a givenlaminar flow section with the upstream ends of two laminar flow sectionassociated with a successive filtration stage, when there is asuccessive stage, and having an impact target at the junction of thedownstream end of the laminar flow section and said connecting passage;said entrance means conducting fluid to said fluid flow passages andsaid exit means conducting fluid from the final filtration stage out ofthe filter body.
 12. A filter having a plurality of successivefiltration stages therein for purifying fluid flow comprising: a platehaving entrance and exit means for fluid flow; a plurality of individuallaminar flow channels formed on said plate, all such channels beingsmooth and of sufficient length to permit fluid reaching the downstreamends thereof to develop laminar flow characteristics; a plurality ofconnecting channels on said plate, each of said connecting channelsintersecting the downstream end of an individual laminar flow channeland having an impact target surface at the intersection, each connectingchannel extending to the upstream end of a successive laminar flowchannel whEn a successive laminar flow channel is present; said entrancemeans conducting fluid to the laminar flow channels associated with afirst filtration stage and said exit means conducting fluid from theconnecting channels associated with a final filtration stage out of theplate; and closure means cooperating with said plate to form closedpassages of the channels on said plate.
 13. The combination according toclaim 14 wherein each of said connecting channels forms an arc of acircle, connecting channels of successive stages having their arcsconcentric.
 14. The combination according to claim 12 wherein portionsof each connecting channel form arcs of circles, the arc portions of theconnecting channels of successive stages being concentric.
 15. Thecombination according to claim 12 wherein said plate is annular and saidlaminar flow channels are arranged radially thereon.
 16. A filter with aplurality of successive filtration stages therein for purifying fluidflow comprising: a filter body having entrance and exit means for fluidflow; a plurality of individual laminar flow passages in the body saidpassages being smooth and of sufficient length to permit fluid reachingthe downstream ends thereof to develop laminar flow characteristics;means in said body providing connection between the upstream ends of twolaminar flow passages associated with a successive filtration stage,said means intersecting the downstream end of an individual laminar flowpassage, an impact target surface being formed by the intersection ofsaid connection means with said downstream end of said laminar flowpassage; and said entrance means conducting fluid to the laminar flowpassages associated with a first filtration stage, and said exit meansconducting fluid from the connecting passages associated with a finalfiltration stage out of the said filter body.
 17. A filter having aplurality of successive filtration stages therein for purifying fluidflow comprising: a plate having entrance and exit means for fluid flow;a plurality of individual laminar flow channels formed on said plate,all channels being substantially straight and of sufficient length topermit fluid reaching the downstream ends thereof to develop laminarflow characteristics; a plurality of connecting channels on said plate,each of said connecting channels intersecting the downstream end of anindividual laminar flow channel and having an impact target surface atthe intersection, each connecting channel extending between the upstreamends of two laminar flow channels associated with a successivefiltration stage when a successive filtration stage is present; saidentrance means conducting fluid to the laminar flow channels associatedwith a first filtration stage and said exit means conducting fluid fromthe connecting channels associated with a final filtration stage out ofthe plate; and closure means cooperating with said filter plate to formclosed passages of the channels on said plate.
 18. A filter washer foruse with a plurality of other like washers which, when aligned andcompressed collectively form a stacked washer filter element with aplurality of successive filtration stages on each washer for purifyingfluid flow comprising: said washer having substantially flat first andsecond surfaces with a core extending therebetween and terminating ateach of said surfaces, said core spaced from the outer edges of saidplate; a plurality of individual laminar flow channels of sufficientlength to permit fluid reaching the downstream ends thereof to developlaminar flow characteristics, said laminar flow channels located on saidfirst surface of said plate; a plurality of connecting channels on saidfirst surface of said plate, each of said connecting channelsintersecting the downstream end of an individual laminar flow channeland having an impact target surface at the intersection and eachconnecting channel extending between the Upstream ends of two laminarflow channels associated with a successive filtration stage when asuccessive filtration stage is present; means conducting fluid to thelaminar flow channels associated with a first filtration stage, and fromthe connecting channels associated with a final filtration stage out ofthe said filter washer plate; and all of the channels, conducting means,and impact target surfaces on said first surface of said platecooperating with the flat second surface of a like plate to form closedpassages across the said plate when two like plates are aligned andcompressed.